The present invention relates generally to instruments and techniques for less-invasive cardiac valve repair or replacement, and more particularly to instruments and techniques which employ thermal energy for repairing or replacing cardiac valves.
As illustrated in FIGS. 1 and 2 of the attached drawings, the heart has four chambers (the left 11 and right 13 ventricles, and the left 15 and right 17 atria) and four valves (the aortic 19, mitral 21, tricuspid 23, and pulmonary 25 valves) which provide unidirectional flow of blood either from one chamber of the heart to another chamber, or from one chamber to a greater vessel (e.g., aorta 63, superior vena cava 61, inferior vena cava 65, pulmonary artery 67, etc.) of the heart, or from a greater vessel to a chamber. The left 15 and right 17 atria are thin-walled filling chambers which provide only a small amount of pumping force while the left 11 and right 13 ventricles have thick muscular walls for pumping blood out of the heart. The position of the valves is as follows: the mitral valve 21 is between the left atrium 15 and the left 11 ventricle; the aortic valve 19 separates the left ventricle 11 from the aorta; the tricuspid valve 23 is between the right atrium 17 and the right ventricle 13; and the pulmonic valve 25 separates the right ventricle 13 from the pulmonary artery.
The blood circulation process is as follows. Blood circulates from the heart through the body""s arterial system to provide oxygen to the body, and then returns with carbon dioxide through the venous system, which culminates in the superior and inferior vena cava at the coronary sinus, and into the right atrium. When the right ventricle is relaxed, blood is pumped by the right atrium through the tricuspid valve into the right ventricle. When the right ventricle contracts, blood is pumped from the right ventricle through the pulmonic valve to the pulmonic trunk and into the lungs where it becomes reoxygenated. The oxygenated blood then returns to the left atrium via the pulmonary veins and is pumped by the left atrium through the mitral valve into the left ventricle. Blood is then pumped by the left ventricle across the aortic valve into the aorta and onto the body""s arterial system to repeat the process.
In a normal functioning heart, the four valves operate synchronously as shown with reference to FIGS. 2A and 2B. During systole, when the left and right ventricles contract, the mitral 21 and tricuspid 23 valves close and the aortic 19 and pulmonic 25 valves open to allow blood to flow from the heart to the body and lungs, respectively. During diastole, when the ventricles return to their uncontracted state, the mitral 21 and tricuspid 23 valves open to allow blood to flow from the left and right atria into the left and right ventricles, respectively, while the aortic 19 and pulmonic 25 valves close to prevent blood from flowing from the aorta and pulmonary artery. respectively, back into the heart.
The four heart valves fall into one of two categories. The mitral and tricuspid valves are similar in structure and are referred to as atrioventricular valves, so defined as each separates corresponding atrial and ventricular chambers of the heart. The aortic and pulmonic valves, which are structurally similar to each other but differ greatly in structure from the mitral and tricuspid valves, are known as arterial or semilunar valves.
The atrioventricular valves are each comprised of several collagen-based anatomical components including a number of leaflets or cusps, an annulus, chordae tendineae, and papillary muscles. The leaflets are thin, yellowish-white membranes with fine, irregular edges which define one or more leaflet cusps which converge with adjacent cusps by commisures. The leaflets originate from the valve""s annulus which is a fibrous ring around the valve and has a circumference typically in the range between about 8.5 cm and about 10 cm.
The mitral valve has a D-shaped annulus which encircles two leaflets to define a generally bicuspid configuration. The anterior or aortic leaflet is large than the posterior or mural leaflet, the latter having a triscalloped configuration with a large middle cusp between two smaller commissural cusps. The tricuspid valve, as implied by its name, generally has three leaflets consisting of an anterior, a medial (septal), and one (or two) posterior cusps. The commisures of both of these valves have variable depths between the cusps and never reach the annulus resulting in the cusps being only incompletely separated from each other. Upon closure of the atrioventricular valves during systole in a healthy valve, the free edge of each leaflet cusp presses against that of an adjacent leaflet or leaflets, resulting in a secure, fluid-tight closure.
Within the walls of each ventricle are the papillary muscles which act as anchors for tendonous cords, i.e., the chordae tendineae, which are attached at their opposite ends to the leaflets of the mitral and tricuspid valves. The chordae tendineae are divided into three groups. The first two groups of chordae originate from or near the apices of the papillary muscles. They form a few strong, tendinous cords which subdivide into several thinner strands as they approach the leaflet edges. The chordae of the first group insert into the extreme edges of the leaflets by a large number of very fine strands. A major function of the chordae is to prevent the opposing borders of the cusps from inverting. The chordae of the second group insert on the ventricular or under surface of the cusps, approximately at the level of the noduli Albini, tiny nodules at the edge of the cusps. This second group of chordae function as the mainstays of the valves and are comparable to the stays of an umbrella. The third group of chordae originate from the ventricular wall much nearer the origin of the cusps and insert into the underside of the base of the posterior leaflet. These chordae often form bands or fold-like structures which may contain muscle tissue.
The arterial or semilunar valves, i.e., the aortic and pulmonic valves, differ greatly in structure from the atrioventricular valves. The former consists of three pocket-like leaflets, also collagen-based, of approximately equal size. Unlike the artrioventricular valves, the arterial valves do not have a well-defined annulus of fibrous tissue, but instead, the leaflets originate from the arterial wall within which the respective valve sits. For the aortic valve, this is the aorta, and for the pulmonic valve this is the pulmonic artery. The pulmonic valves generally have a diameter ranging from about 19 to 37 mm. The leaflets of these valves expand into three dilated pouches known as the sinuses of Valsalva. The leaflet cusps are largely smooth and thin, and each have, at the center of their free margins, a small fibrous nodule called the nodulus Arantii. On each side of this nodule, along the entire free edge of the cusp, there is a very thin, half-moon-shaped area termed the lunula (hence the name xe2x80x9csemilunarxe2x80x9d). Unlike the atrioventricular valves, the arterial valves do not have any chordae tendinaea or papillary muscles.
There are various types of acquired diseases or congenital anomalies which can effect one or more of the above-described anatomical components of a cardiac valve such that the valve does not completely or properly open or close. As a result, a valve (i.e., the aortic or pulmonic valve) may restrict blood flow out of the heart during systole, or alternately a valve (i.e., the mitral or tricuspid valve) may allow blood flow back into the heart during diastole. The diseases or anomalies fall within two general categories of pathologies of the valves: stenosis and insufficiency. A stenotic valve is one that does not open properly or allow normal forward blood flow, and an insufficient valve is one that does not close properly or which allows retrograde leakage of blood.
Stenosis of the valve, often characterized by a narrowing of the valve orifice, is typically the result of an acquired disease, most commonly either rheumatic heart disease or arteriosclerosis, but may also result from a congenital defect. With rheumatic heart disease (also known as rheumatic endocarditis), vegetative lesions tend to form on the cusps along the line of closure of the valve. This leads to a fusion of the commisures of the leaflets, reducing the amount of blood flow through the valve. The mitral and aortic valves are the most likely to be affected by this condition, whereas the tricuspid valve is infrequently affected, and the pulmonic valve is rarely affected.
Arteriosclerosis, commonly known as coronary artery disease, is another common cause of stenosis of the cardiac valves. Arteriosclerosis involves a calcification or a build-up of plaque within the coronary arteries which in turn deprives at least a portion of the myocardium of oxygen. The collagenous tissue that forms cardiac valves is highly dependent upon oxygen to maintain its integrity and, when oxygen is not supplied, these tissues will stretch, destroying valvular competency. Particularly, the mitral valve annulus is susceptible to dilation, changing its normal D-shaped or elliptical geometry to a more circular configuration.
Calcification may also occur directly on the valve itself. Unlike the rheumatic lesions, calcium deposits form primarily on the annulus. This may result in a reduction of leaflet mobility and an increase in tension on the chordae which in turn results in elongation of the chordae. Annular calcification frequently occurs in patients with hypertension or metabolic diseases, such as diabetes, but may also result from congenital disorders such as a prolapsed or billowing leaflet, a bicuspid aortic valve (which does not open as widely as a normal aortic valve with three cusps), or disorders of the connective tissue, such as Marfan""s syndrome.
The other primary valve pathology, valvular insufficiency, involves improper closure of the valve, causing regurgitation, or the back flow of blood through the valve. As with valvular stenosis, insufficiency of the valves may result from acquired or congenital diseases. Most commonly, this defect is seen in the mitral valve where blood returns through the valve back into the left atrium during systole due to a xe2x80x9cprolapsexe2x80x9d of the leaflet. Commonly known as mitral valve prolapse (also known as MVP or xe2x80x9cclick-murmerxe2x80x9d syndrome), the leaflets and chordae become affected by a process called myoxmatous degeneration wherein the structural protein and collagen fibers form abnormally causing a thickening, enlargement, or redundancy of the leaflets and chordae. When the ventricle contracts, the redundant leaflets prolapse (flap backwards) into the atrium, allowing backward leakage or regurgitation of blood through the valve opening. If significant, this condition may result in abnormal heart rhythms, endocarditis (infection of the valve), enlargement of the heart, and an imbalance of the autonomic nervous system.
Various surgical techniques have been used to replace, repair or restructure a diseased or damaged cardiac valve. Each technique has its own complexities, advantages, and disadvantages. Most diseased semilunar valves are replaced rather than repaired because their function can be easily simulated with a replacement prosthesis and because the typical types of damage to these valves is not easily repairable. On the other hand, most atrioventricular valves are preferably repaired rather than replaced. This is so because it is difficult to simulate the function of the chordae tendineae of the atrioventricular valves in a replacement prostheses, and often, these valves can be brought to their proper function by the removal of excess valve tissue.
Valve replacement involves excising the valve leaflets of the natural valve, and securing a replacement valve in the valve position, usually by suturing the replacement valve to the natural annulus. The types of replacement valves include mechanical prostheses, biological prostheses, and allografts (transplant of a valve from a donor cadaver, and transplant of the pulmonic valve to the mitral position).
There are currently three widely used types of mechanical prostheses: the Starr-Edwards ball-in-cage valve, the Medtronic-Hall tilting disc valve, and the St. Jude bileaflet valve. As with all valve replacement procedures, replacement with a mechanical valve first involves excising the natural valve from the heart. Especially with the mitral valve, this is a delicate task as excess excision, particularly posteriorly, can result in deficient tissue for suture placement or in complete detachment of the atrium from the ventricle. The natural annulus is then sized with a sizing, instrument. After the size has been determined, a valve is then selected for a proper fit. Proper sizing is important as an oversized replacement valve can cause coronary ostial impingement or tearing of the natural annulus. On the other hand, an undersized valve will reduce flow volume and cardiac output. Next, sutures are placed in the natural valve annulus which has been properly prepared after removal of the leaflets and, in some mitral or tricuspid valve replacement cases removal of, the chordae tendineae. Various suture techniques may be used, including simple interrupted, interrupted vertical mattress, interrupted horizontal mattress with or without pledgets, or continuous, depending on the anatomical valve being replaced, the brand of mechanical valve, and the particular patient anatomy. Regardless of the specific suturing technique employed, this step is crucial to the outcome of the replacement procedure, requiring accurate and flawless suturing. After placement in the natural annulus, the same sutures are placed through the mounting cuff, the valve is seated into the annulus, and the sutures are tied and with the excess suture length cut.
Although mechanical valves have proven to be extremely durable and can be expected to last from 20 to 40 years, they all require life-long anticoagulation with blood thinners to prevent clot formation on the valve surfaces. These replacement valves have the further disadvantage in that the mounting cuffs or rings occupy space, narrowing the effective orifice area of the valve and reducing cardiac output.
Biological prosthetic valves, such as those processed from pigs (porcine) or cows (bovine), have the advantage of not requiring the patient to take life-long anticoagulation medication or requiring a mounting prostheses. However, the average life expectancy for such bioprostheses is only from about 8 to 10 years. Therefore, bioprostheses are primarily used in older patients or in patients who cannot tolerate blood thinners. Recently, valves from human cadavers have been used in younger patients to avoid the need for anticoagulation medication, however, the availability of human grafts is limited with long-term outcomes still unknown.
For these reasons, it is sometimes preferable to repair rather than replace a cardiac valve. Valve repair techniques which involve the removal or reduction of some portion of the valve include: annuloplasty (contracting the valve annulus), leaflet resection (narrowing the valve leaflets), and shortening the mitral or tricuspid valve chordae tendineae. Prosthetic ring annuloplasty is commonly performed to reduce a dilated valve annulus, most commonly in the mitral valve. This procedure involves suturing a semirigid ring to the natural annulus of the valve. The selective rigidity of the ring allows the surgeon to reshape the annulus to its normal elliptical configuration while maintaining an optimal orifice area.
Resection of the leaflet is performed when a leaflet is prolapsed due to an elongated or ruptured chordae. Repair is achieved by excision of a portion of the leaflet. The open portion of the leaflet is then sutured closed and stay sutures are placed around the normal chordae adjacent to the prolapsed portion of the leaflet.
An elongated chordae can be corrected by folding the excess length of the chordae into an incised trench made in the papillary muscle. After the trench is made a suture is placed through half of the trench, around the elongated chordae, and then through the other half of the trench. Enough traction is placed on the suture so that the excess length of the chordae is pulled into the trench in the papillary muscle, thus wedging the resection of the papillary muscle to shorten the chordae at which point the trench is sutured closed, trapping the excess chordae inside.
The above valve repair techniques, when properly performed, can result in low operative mortality, improvement in ventricular function low incidence of thromboembolism, low incidence of reoperation, and lasting(g improvement in hemodynamics. However, these procedures can be extremely complex, particularly in patients requiring more than one valve repair procedure, such as a combination of annuloplasty and leaflet resection. Often, only the most highly skilled cardiac surgeons are successful at these valve repair procedures. A particularly prevalent cause of reoperation in valve repair procedures is caused by shortening of the chordae which results in a poor fit of the valve or valve leaflets and may result in prolapse or regurgitation of the valve.
Conventionally, the repair or replacement of a heart valve is accomplished through a median sternotomy (most typically for an aortic valve procedure) or major thoracotomy (most typically for a mitral valve procedure), requiring(g general anesthesia and total cardiopulmonary bypass (CPB) with cardioplegic arrest. These procedures are highly traumatic and have significant complications associated with the median sternotomy or major thoracotomy, resulting in a prolonged, painful, and expensive recovery. Such procedures tend to involve a large number of instruments and sutures, making access via an invasive incision unavoidable. Additionally, typical conventional valve procedures require the patient to be on a CPB xe2x80x9cpump runxe2x80x9d and have cross-clamping of the aorta (the ill effects of both which are well known and documented) for at least an hour in replacement procedures and about an hour and a quarter for repair procedures. These times arc further increased for surgeries involving more than one repair or replacement procedure and/or the repair or replacement of the repair or replacement of more than one valve.
Less-invasive and endoscopic devices and methods have been developed which eliminate the need for an invasive incision. However, small or endoscopic incision sites and instrumentation increase the complexity of the surgery and increase the already lengthy pump runs and cross-clamp times.
What is needed, therefore, are devices and methods for carrying out heart valve replacement and repair, as well as other procedures in the heart, which eliminate the complexities associated with current techniques, reduce the pain and trauma to the patient, and reduce the time which the patient is on CPB and cross-clamping. The present invention fulfills these needs, and provides further related advantages, as will become apparent from the following description and accompanying drawings of the invention taken in conjunction with the appended claims.
The present invention provides devices and methods for performing surgical procedures which involve the thermal contraction or shrinking of collagen-based tissue in the heart, and more particularly which involve the thermal reduction of collagen-based tissue of the heart valves to improve the function of a diseased or defective valve.
Collagen molecules consist of three polypeptide chains arranged in a parallel triple-helix. The individual polypeptide chains are called alpha-chains, and each is approximately 1000 amino acid units in length. This results in an average diameter of 14 xc3x85 and an average length of about 300 nm for a single collagen molecule. The helical conformation of each chain is dependent on the fact that every third unit is glycine with hydroxyproline and proline recurring very frequently. Cross-linking occurs between the sides of the collagen molecules. These intermolecular cross links provide collagen tissue with the unique physical properties of high tensile strength and substantial elasticity.
When subject to elevated temperatures, the collagen cross links rupture resulting in an immediate contraction or shrinking of the collagen fibers. This shrinkage takes place in a direction parallel to an axis of collagen fibers and can result in as much as a ⅔ reduction in the fibers"" original length. Additionally, the diameter of the individual fibers increases greatly, over four fold, without changing the structural integrity of the tissue.
The thermal shrinking of collagen connective tissue is a known technique in orthopedic applications, such as in the repair of ligaments and joint capsules. U.S. Pat. No. 5,458,596 to Lax et al discloses the use of radiofrequency (RF) energy for the controlled, non-ablative thermal shrinking of collagen-based tissue in orthopedic applications. What has not previously been contemplated, however, is the use of non-ablative thermal energy to shrink or contract collagen-based tissue in the heart, and particularly for the repair of diseased or defective heart valves requiring the removal or contraction of tissue, or for facilitating the attachment of a replacement valve.
Accordingly, a general object of the present invention is to provide methods and instruments for the application of thermal energy to a tissue site in the heart which is comprised of collagen.
The teachings of the present invention include an apparatus for supplying thermal energy to a diseased heart valve structure comprising an elongate member having a distal end and a proximal end, including a thermal heating member fixed to the distal end of the elongate member, and at least one thermal heating element adapted to supply thermal energy to a diseased heart valve structure disposed on the thermal heating member. An energy source in communication with the thermal heating element is also provided for supplying thermal energy to a target location on the valve structure. Preferably, the thermal heating element is an electrode in electrical communication with the power source.
An apparatus for providing thermal energy to a valve structure may also include additional components, including: an integrally formed endoscope configured to allow visualization of an area of interest of the diseased heart valve structure; a vacuum lumen adapted to connect an external vacuum source with a vacuum port disposed on the distal end of the elongate member; and a fiber-optic illuminator adapted to provide illumination of the diseased heart valve structure. Generally, the thermal heating member includes at least one thermal heating element and may include one or more additional structures such as described above.
In a preferred configuration of the present invention, the apparatus includes a controller configured to selectively control the intensity and duration of thermal energy supplied to the thermal heating element; a temperature sensor adapted to monitor the temperature of the thermal heating element; and a feedback control device configured to receive temperature data from the temperature sensor and adjust the supply of energy to the thermal heating element so as to maintain the temperature of the thermal heating element within a preselected temperature range. In this manner, the treatment temperature may be controlled to prevent ablative damage to the treated tissue.
A variety of configurations are appropriate for the thermal heating member, including a transverse groove sized to accommodate a diseased chordae wherein the at least one thermal heating element is disposed on an inner surface of the groove; a hook member sized to engage the chordae, wherein the at least one thermal heating element is disposed on an inner surface of the hook member. The thermal heating member may be configured to be conformable to allow adjustment of the device for different clinical applications.
In one embodiment, the apparatus of the present invention is configured to be endoscopically inserted to region of interest and includes a trocar insertion sleeve configured to slidably receive the elongate member and the thermal heating member, wherein the heating member is adapted to be disposed within the trocar insertion sleeve. In one configuration, the apparatus includes a thermal heating member comprising a flexible panel member configured to be rolled lengthwise when disposed within the trocar insertion sleeve. The device may also be made steerable to facilitate insertion and manipulation of the device.
The teachings of the present invention include an apparatus configured to supply thermal energy to a diseased annulus wherein the thermal heating member comprises an annular configuration sized to approximate the circumference of a diseased annulus. In such a configuration, the thermal heating member includes a plurality of thermal heating elements disposed about a circumference of the annular configuration as well as additional structures. Alternatively, the apparatus may be configured to allow beating heart repair of a diseased annulus or leaflet without interfering with the functioning of the treated valve. A preferred embodiment of an apparatus for repairing a diseased valve structure is configured to be endovascularly inserted in a contracted configuration to a region of interest proximate a valve to be treated. The apparatus configured to be expanded for treatment of the valve structure.
Another embodiment of a device for providing thermal energy to a diseased valve structure comprises a thermally conductive suture configured for installation in the valve structure to be treated, and a power source in communication with the thermally conductive suture.
The teachings of the present invention include devices for the replacement of a diseased heart valve utilizing thermal energy supplied to the annulus of the diseased valve. A preferred device comprises an elongate member having a distal end and a proximal end, a thermal heating member configured to provide thermal energy to the annulus of a diseased heart valve fixed to the distal end of the elongate member, and at least one thermal heating clement disposed on the thermal heating member. The device also requires an energy source in communication with the thermal heating clement. The device may also include a valve holder configured to fix a prosthetic valve to the distal and of the elongate member.
The present invention also includes methods of repairing a diseased valve using the application of thermal energy to the diseased valve structure. A preferred method comprises the steps of a) providing a working space proximate the diseased heart valve structure, and b) providing non-ablative thermal energy to the diseased valve structure so as to selectively contract the diseased heat valve structure. Preferably, the step of providing non-ablative thermal energy to the diseased valve structure comprises the steps of contacting the diseased heart valve structure with a thermal heating element, and providing thermal energy from the thermal heating element to the diseased valve structure so as to selectively contract the diseased heart valve structure.
The step of contacting the valve structure with the thermal heating element may comprises a number of alternate methods, including installing at least one thermally conductive suture in the valve structure to be treated. The valve structure contacted includes a diseased chordae, a diseased annulus, or a diseased or misfitting valve leaflet.
In a preferred method of the present invention, the heart function is monitored concurrently with treating the diseased valve structure so as to receive feedback on the treatment effect. In one method, the monitoring device comprises a transesophegial echocardiography device, the method including the additional step of installing the device so as to monitor the functioning of the diseased heart valve.
A number of access procedures are suitable for use with the teachings of the present invention, including: a thoracotomy, a sternotomy, a mini-thoracotomy, a thorascopic access procedure, a mini-sternotomy, a sub-xyphoid access procedure, a xyphoid access procedure, and an endovascular access procedure. The teachings of the present invention are suitable for use with both beating heart and stilled heart procedures.
The teachings of the present invention include methods for replacing a diseased valve using thermal energy applied to the valve annulus. A preferred method of replacing a diseased heart valve comprises the steps of a) providing a working space proximate the diseased heart valve; b) excising the leaflets of the natural heart valve; c) inserting the prosthetic heart valve into the annulus; d) contacting the annulus with a thermal heating element; e) providing thermal energy from the thermal heating element to the annulus to selectively contract the annulus about the prosthetic heart valve; and f) continuing to provide thermal energy to the annulus until the prosthetic heart valve is securely engaged within the annulus.